A check valve is generally defined as a valve that permits flow in one direction but prevents flow in a return direction. One type of check valve has a housing that defines an axially extending cavity divided by a valve orifice into a first portion and a second portion. The two portions communicate with first and second ports, respectively. A valve member is urged against a seat surrounding the orifice by fluid pressure in the first port and moved away from the seat by fluid pressure in the second port. In some circumstances, it is desirable to provide a means for mechanically opening the valve when the pressure in the first port is higher than the pressure in the second port. A simple way of accomplishing this is to provide a control member that engages the valve member and can be pulled to mechanically move the valve member away from the seat. A problem that arises in connection with this type of arrangement is that a high level of force is required to overcome the pressure differential between the two ports and unseat the valve member. The high level of force, in turn, requires that the control member be heavy duty so that it is capable of carrying the required force.